Candidate Members of the VMP/EMP Disk System of the Galaxy from the SkyMapper and SAGES Surveys
arxiv(2023)
摘要
Photometric stellar surveys now cover a large fraction of the sky, probe to
fainter magnitudes than large-scale spectroscopic surveys, and are relatively
free from the target-selection biases often associated with such studies.
Photometric-metallicity estimates that include narrow/medium-band filters can
achieve comparable accuracy and precision to existing low-resolution
spectroscopic surveys such as SDSS/SEGUE and LAMOST. Here we report on an
effort to identify likely members of the Galactic disk system among the very
metal-poor (VMP; [Fe/H] ≤ –2) and extremely metal-poor (EMP; [Fe/H]
≤ –3) stars. Our analysis is based on an initial sample of ∼11.5
million stars with full space motions selected from the SkyMapper Southern
Survey (SMSS) and Stellar Abundance and Galactic Evolution Survey (SAGES).
After applying a number of quality cuts to obtain the best available
metallicity and dynamical estimates, we analyze a total of ∼5.86 million
stars in the combined SMSS/SAGES sample. We employ two techniques that,
depending on the method, identify between 876 and 1,476 VMP stars (6.9
of all VMP stars) and between 40 and 59 EMP stars (12.4
stars) that appear to be members of the Galactic disk system on highly prograde
orbits (v_ϕ > 150 km/s). The total number of candidate VMP/EMP disk-like
stars is 1,496, the majority of which have low orbital eccentricities, ecc ≤
0.4; many have ecc ≤ 0.2. The large fractions of VMP/EMP stars associated
with the Milky Way disk system strongly suggest the presence of an early
forming “primordial" disk.
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